A popular board game called Terraforming Mars explores the many possible methods and mechanisms which would raise the temperature, free water volume and oxygen level on the surface of Mars. This idea - that Mars could be made more Earth-like or terraformed - has been a popular one in science fiction since the genre began, rooted in the historical success of humanity in reshaping its environment around itself. Whether draining malarial marshes, irrigating deserts or modifying entire planetary environments, there was a confident expectation that humans could transform marginally habitable environments into comfortable places to live.

However, for as long as there have been stories of terraforming Mars, there have been writers asking how humanity might react to attempts to areoform (make Mars-like, from Ares - the greek name for the Roman God Mars) or more generally xenoform Earth.

The Chances of Anything Coming from Mars

Arguably the first example in this genre traces back to H G Wells and his The War of the Worlds (1897). In this best-selling novel, and its many adaptations, an invading Martian force starts to spread a Red Weed which suppresses native life and acts as a modifying force, rendering Earth more Mars-like. In the original novel, it is left ambiguous whether the introduction of the Red Weed is deliberate, or an example of a biocontaminant which was carried unwittingly by the ships, although later adaptations have tended to imply its introduction was deliberate.

All down the line from there the aspect of the country was gaunt and unfamiliar; Wimbledon particularly had suffered. ... The Wandle, the Mole, every little stream, was a heaped mass of red weed, in appearance between butcher’s meat and pickled cabbage. (part 2, chap IX)

The red weed has proved a potent image of the impact of alien invasion not just on humanity but on our entire environment. From radio play adaptations of War of the Worlds to modern graphic novels such as Scarlet Traces, descriptions of the weed, its effects and the way it smothers native Earth life has provoked horror and a sense of alienation which mirrors the desolation experienced by the characters.

Figure (right): The red weed as a powerful emblem of areoforming overwhelming the traditional buildings of the English countryside, illustrated in one of the original art works commissioned for the release of Jeff Wayne's 1978 War of the Worlds concept album. This art spread by Geoff Taylor.

To nineteenth- and early twentieth- century readers in Britain, the idea of a technologically advanced race coming to their country and modifying their environment in ways which compromised their lifestyle was deeply shocking. Many commentators both at the time and more recently have noted the irony of this: at the time, Britain was an imperial power which did exactly that in many places around the world. While Wells generally saw British culture as a civilising and positive influence, there is no doubt that he was also commenting on the dangers of abusing a power imbalance, and inviting audiences to consider how they would react to having such an environmental modification imposed upon them - whether deliberately or otherwise.

A more certainly deliberate attempt at areoforming Earth by native Martians can be found in the early years of Doctor Who. The series’ second unfortunate moonbase finds itself invaded by the Ice Warriors in “The Seeds of Death” (1969, the first had endured an assault by Cybermen two years before). Ice Warriors - a reptilian race adapted for cold temperatures and low oxygen levels - are the canonical original residents of Mars in the Doctor Who universe. Their assault on the moon was merely the prelude to a more ambitious plan. Using the transmat (i.e. teleportation) technology based there, they distributed a lifeform around Earth which spread as a kind of foam, absorbing oxygen as it went. This was a deliberate and calculated attempt to reduce the amount of free oxygen in Earth’s atmosphere, rendering it into a more habitable environment for the Martians… and a less habitable environment for native Earth life. Only a risky sample collection (shown in the image) and scientific analysis finds a solution.

Figure (left): Patrick Troughton's Second Doctor collects a sample of the foam-like fungus overwhelming an Earth ecosystem and modifying its atmosphere in Doctor Who: The Seeds of Death. Note the bubble of toxic low-oxygen air about to burst in the foreground.

Both these renditions of Martians shared the common view of the time that Mars was an old planet, its civilisations ancient and its conditions deteriorating. The distance of Mars from the Sun and its thin atmosphere (already recognised at the time) means that energy is in low supply there - whether extracted directly from the Sun or processed via plant life. For hypothesised Martian aliens, moving Sunwards was the best way of finding a more habitable environment - although in at least the former case they discovered that unfamiliar biospheres can carry invisible threats in the form of microorganisms.

Indeed microorganisms of one kind or another are likely to be far more efficient survivors than any more complex life. This is a threat to other potential ecosystems as well as our own - a large part of the human effort involved in building planetary landers these days is dedicated to ensuring that biological contamination (such as that which may be represented by the Red Weed) is avoided!

The Poison Skies

However Martians are not alone in attempting to modify Earth’s environment to suit themselves in science fiction. A number of other alien races have attempted to modify Earth’s atmosphere to better match their own requirements - i.e. to xenoform (i.e. make “other”) the planet.

An interesting, although never-actualised, plan to xenoform Earth was undertaken by the titular aliens of John Christopher’s The Tripods Trilogy of juvenile novels (1967-1968). In this post-invasion scenario, human societies have been reduced to a low technology level and live under the electronically-enabled mental control of “The Masters”. Initially appearing only as unseen antagonists housed in their three-legged machines, the later books (particularly The City of Gold and Lead) develop the characters of these aliens and reveal that their goal is the xenoforming of Earth. While they will be unable to increase the planet’s gravity to suit their preferences, they plan to modify the atmosphere to match the thick, green fog maintained in their domed cities, and also to raise the global temperature. The composition of this atmosphere is never discussed although the colour and its toxicity to humans suggests an ammonia or chlorine based gas mixture. Fortunately for the enslaved human population, a group of freedom fighters are able to destroy the alien beachhead before the xenoforming process gets underway.

Moving forward to the mid-nineties, the SF-conspiracy-thriller film The Arrival (1996, starring Charlie Sheen, beware similarly named alternatives!) and its sequel Arrival II (1998) was apparently also predicated on an alien attempt to modify Earth’s environment, this time through a stealth infiltration which aimed to raise the level of greenhouse gases, accelerating the effects of anthropogenic global warming. I must admit that I've never seen this one myself. The film received mixed reviews and it suffers a little from a modern perspective from offering a confused message on climate change. While the story stresses the potential risks of global warming, by conflating it with an alien conspiracy the sense that humanity must take responsibility for its actions (and make lifestyle changes to reduce climate change) is undermined.

And again, Doctor Who provides an example here. In 2008, the Doctor encountered a plot by the Sontarans: having lost their cloning planet, they attempt to saturate Earth’s atmosphere with clone food by the emission of gases from devices fitted to cars (“The Sontaran Stratagem/The Poison Sky”) - this will have the joint effect of allowing them to use the Earth as a site for reproduction while simultaneously killing off the human population. As the image to the left shows, the episodes used the effective (and fairly frequently-used in DW) tool of apparently-authorative BBC-branded news reports [1] which show iconic buildings swamped amidst the toxic gas. Thus human achievements are shown overwhelmed by the xenoforming effort. The project in this storyline actually comes close to succeeding, with the pollution reaching lethal levels in cities and forming a thick brown fog which makes the characters cough. Fortunately, the bulk of the gases are mostly confined to the upper atmosphere and flash-burn without toxic products, enabling the Doctor to intervene and remove the threat.

This story is notable in the way it harnesses fear of the very real issue of human pollution while also warning viewers against assuming an easy fix to anthropogenic climate modification is possible. The Sontaran plan is able to proceed as far as it does due to the near-universal adoption of a (literally) too-good-to-be-true anti-pollution device on vehicles. In defeating the plan, the Doctor saves the planet, but at the same time is forcing humanity to recognise that they’re going to have to come up with their own alternate solutions in future.

Soil and Ocean

Having addressed air, let’s turn our attention to earth. Tade Thompson’s recent Wormwood Trilogy of novels (Rosewater - 2016, Rosewater Insurrection - 2019, Rosewater Redemption - 2019) involves an alien infiltration which includes spreading a form of microbial life similar to fungal spores which are capable of infiltrating both the wider ecosystem and the human nervous system and modifying it to host alien consciousness. These spores are known as xenoforms and represent a deliberately-released invasive species. While the additional effect of forming a form of mental internet is accidental and incidental to the goal of modifying the Earth’s native biology, it nonetheless has a dramatic effect on human populations. Much of the narrative is centred on events in Nigeria, and this trilogy has been positioned within the african futurism genre. I’m by no means an expert in this area, and not qualified to comment on the themes in detail, but it’s worth noting the different perspective it provides on the alien colonialism which forms such a theme in xenoforming narratives.

A final, very different take on xenoforming Earth - this time addressing water - can be found in John Wyndham’s novel The Kraken Wakes (1953). Unlike the stories mentioned above which focus on Earth’s atmosphere and terrestrial biosphere, this story considers an alien race which evolved at high submarine pressures and which seeks to colonise Earth’s deep ocean trenches.

While at first sight, this might not seem to require conflict with humanity, underwater mining by the aliens and deliberate melting of the ice caps cause a dramatic sea-level rise and modify the deep ocean currents that regulate Earth’s surface climate. As a scientist character notes: “having settled into the environment best suited to them, these creatures’ next thought would be to develop that environment in accordance with their ideas of what constitutes a convenient, orderly, and, eventually, civilized condition.”

Military action from humans (atomic bombing of the deeps) is met by sinking of commercial and passenger shipping, and then by “shrimping” expeditions where the aliens harvest the surface-dwellers from coastal villages. By the end of the book, major cities including London have been flooded and human civilisation is crumbling. The aliens have successfully reshaped a large part of Earth to better suit themselves - despite the best humanity could do to prevent it.

Xenoforming as an Object Lesson

Ultimately, narratives of xenoforming serve a number of distinct purposes in science fiction. In particular:

• First and foremost, in their fictional role, they present a challenge that must be overcome by the protagonists and which (usually) can be overcome given sufficient courage and/or scientific knowledge.
• At the same time, they undermine the arrogance of readers in presuming that their technology, culture and lifestyle are superior… or even worthy of notice by the intruders.
• They question the ethics of human environment modification - whether on Earth or planned elsewhere - by placing humans as the subjects rather than originators of the change.
• They highlight the fragility of the only naturally habitable environment we currently know of: Earth’s biosphere.

 As a result, they feed into dialogues regarding the scientific ethics and risks of environment modification which now extend beyond direct impact on humans or similar sentient life. Increasingly, Earth ecosystems already show evidence for the impact of invasive “alien” (meaning foreign rather than extraterrestrial) species which can devastate new environments. As I mentioned above, the novel of The War of the Worlds describes this as true of the Martian Red Weed and certainly emphasises the lethal potential of microbial life introduced by accident. Given how early this was recognised, perhaps it’s no surprise that the early Moon-lander astronauts in the Apollo programme were quarantined on their return or that one of the coolest job titles in NASA is that of “Planetary Protection Officer” - responsible both for preventing contamination of Earth by returning missions, and for ensuring that space probes are decontaminated before launch so as to protect the pristine environments they may encounter.

Nonetheless, the conversation continues. Within the last few years extremophile tardigrades from Earth have been deliberately deposited on the Moon (albeit the plan was for a sealed container and dormant state, but compromised by a probe crash). The New Space movement has also begun pushing once more for human colonisation of Mars, which together with its practical problems again poses questions regarding whether it is ethical to terraform even a sterile environment to suit ourselves. Science, like science fiction, has no clear idea of the answers to these questions, but they are important ones to consider, and - as always - science fiction provides a useful arena in which to explore possible outcomes.

[1] It's worth noting that one of the most famous adaptations of War of the Worlds (the radio play of Orson Wells, 1938) also used mock news reporting as a tool to add verisimilitude, despite its absence from the original novel text. [return to text]

This article uses more technical terminology than most, so I thought I'd provide a short glossary: